In a VoIP (Voice over IP) application, the upstream link may be an asynchronous Ethernet IP link under the RTP protocol (“Real Time Protocol”).
A transmission defect on the upstream link may consist of a loss of IP packets on this link or an absence, at the level of the network element, of frames to be transmitted on the downstream link, said network element possibly being a domestic communication gateway for example.
Two methods for processing this transmission defect are known:                the gateway is equipped with an audio coder and decoder as well as with an error correcting mechanism. The gateway decodes the audio packets received and, if it detects a loss of packets, it activates its error correcting mechanism by generating one or more frames which will be coded then sent on the synchronous downstream link, for example, in replacement for the missing frames. The audio terminal at the end of the synchronous link decodes all the frames received, including the replacement frames, and provides the corresponding audio signal.        when a loss of packets on the upstream link is detected, the network element acting as gateway repeats the last frame that it previously dispatched on the synchronous downstream link for example, doing so as many times as necessary to replace all the frames missing on the latter link.        
However, these known methods making it possible to take account of the transmission defects upstream of the network element exhibit a certain number of drawbacks.
The first method requires the presence of a decoder, of an error correcting mechanism and of a coder at the level of the domestic gateway, in addition to the decoder already present in the audio terminal at the end of the synchronous downstream link. This substantially complicates the architecture of the gateway.
The second method leads to sub-optimal restitution quality on account of the introduction of repetitions of syllables when there are losses on the first upstream link. For example, if the last frame dispatched before the loss of packets is the last syllable “-bile” of the word “automobile”, the gateway may be induced to re-send this syllable several times to fill in the lost frames, thereby resulting after decoding by the terminal in the sound sequence “automobile-bile- . . . ”, which is particularly unpleasant to listen to.